1. Field of the Invention
The present invention relates to a Ball Grid Array (BGA) socket, and particularly to a BGA socket contact having an improved contact pad for securing a solder ball in position.
2. Description of Related Art
BGA sockets are well known in the art for reliably connecting an integrated circuit (IC) module to a circuit board. Such BGA sockets are disclosed in U.S. Pat. Nos. 6,099,321 and 6,062,890. The conventional BGA socket consists of a base, a cover movably mounted on the base, and a plurality of conductive contacts received in the base. The conductive contacts are fitted in contact passageways defined in the base and each comprises a contact pad oriented parallel to the base. After being mounted to the base, each contact is attached with a solder ball at a bottom surface thereof. The solder balls are secured to the contacts pads in advance, and are adapted to electrically and mechanically connect the contacts of the socket to a printed circuit board (PCB) on which the socket is mounted when the socket and the PCB are together subject to a reflow process. Although the conventional BGA socket has proven to work well, disadvantages exist which need to be addressed. Referring to FIGS. 4A and 4B, the bottom surface 91 of the contact pad 9 of a conventional BGA contact is flat or has only one dimple 92 formed therein. After the solder ball 8 is attached on the contact pad 9, the solder joint between the solder ball 8 and the contact pad 9 is not reliable enough to sustain an external shearing force. Thus, the solder ball 8 may be damaged and even broken off during assembly and/or transportation, thereby adversely affecting the electrical capability of the whole socket.
Hence, a BGA socket with improved contacts is required to overcome the disadvantages of the prior art.
An object of the present invention is to provide a BGA socket with an improved contacts for securing solder balls in position.
Another object of the present invention is to provide a contact with an improved contact pad.
In order to achieve the objects set forth, a BGA socket for electrically interconnecting an IC module and a circuit board in accordance with the present invention comprises a base defining a plurality of contact passageways, a plurality of contacts received in the contact passageways, and a cover movably mounted on the base and defining a plurality of receiving holes for receiving corresponding pins of the IC module. Each contact has a fitting portion fixedly engaging with the base, a contact portion formed above the fitting portion for engaging with a corresponding pin of the IC module, and a contact pad below the fitting portion for being soldered to the circuit board. The bottom surface of the contact pad has a plurality of bumps. A solder ball is soldered to the contact pad by soldering with the bottom surface of the contact pad and the bumps.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.